This code does not show the arrow down

<td style="width: 100px; height: 52px;" valign="top" >
                    <asp:Listbox ID="CheckBoxSalesTypes" runat="server" TextAlign="Left" SelectionMode="Multiple">
                        <asp:ListItem Selected="True" Value="2">Orders</asp:ListItem>
                        <asp:ListItem Value="1">Quotes</asp:ListItem>
                        <asp:ListItem Value="3">Invoices</asp:List ...